1. Field of the Invention
This invention relates generally to electric steering systems for automobiles and, more particularly, to such systems where each wheel is steered electrically and independently of the other wheels.
2. Description of the Prior Art
In typical four-wheel steering systems, the front pair of wheels are interconnected in conventional fashion for synchronized steering movement and are steerable separately from the rear pair of wheels which are similarly connected to each other for synchronized steering movement. Where steering is power assisted, hydraulic and/or electrical actuators steer the pairs of wheels in response to control inputs from an operator controlled implement such as a steering wheel. In automobile four-wheel steering systems, the typical practice is to provide a train of mechanical links between the steering wheel and each of the pairs of steered wheels to assure control in the event that the power assist becomes inoperative. In some vehicle applications where speed is always relatively slow, electro-hydraulic four wheel steering systems have been proposed where no mechanical connection exists between the steering wheel and the steered wheels of the vehicle. In such systems, the four wheels are independently pivotable on the vehicle chassis by respective ones of four hydraulic cylinders which are pressurized and exhausted by an electronic control in response to manual steering inputs from the operator of the vehicle. These systems may lack the rapid response capability required in automobile steering systems and are unprotected if hydraulic assist is lost. A steering system according to this invention represents an improvement over prior systems in that it combines in one system the advantages of independent, electrically powered steering of each of the four wheels of the vehicle with a simple and effective mechanical interlock which maintains acceptable steering control in the event one electric motor of the front or rear pair of motors becomes inoperative.